* Add fuzzer for mpg123_decode.
This fuzzes a different and non-filebased API that read_fuzzer.c.
mpg123_decode is, however, streaming based so we need to chunk the
fuzzer's input into multiple pieces, and pass them to the library. This
is pretty annoying to do by hand so I've introduced byte_stream.h to do
this automatically. Sadly, byte_stream.h is very C++ so the
decode_fuzzer is also C++ now. This isn't ideal since mpg123 is a
C library but this is the easiest way to do it.
* Do not carry next input within std::string.
* Malloc a new buffer for each decode invocation.
I used malloc instead of new since ideally this fuzz target would be
written in C.
Markus Kusano